Hi Melisa,
That's great! I actually 100% agree that you don't want to be the smartest in the room, etc. I just think so much has to do with your district percentiles, and it's better to use those as a gauge than the national numbers. You can better know what to expect from his classmates when you consider your district numbers. These are available on the NWEA reporting sheets, but usually just for the grade your child is in.
I have an older child, so I'm able to look at the MAP NWEA percentiles for different grades, using that history. So you can see that a 247 in math in spring of 5th grade puts your child in the 96th percentile nationally vs. other 5th graders, and it puts him in 91% vs. 6th, and the 82nd percentile vs. 7th graders. You are talking about skipping him up 2 grades in math, so you'd be placing him where he is currently above 82% of the kids doing that math. But if your district is strong, he could be much, much lower than that. For example, in my district, a 248 is only the district AVERAGE (ie 50th percentile) for 7th graders. So here, someone moving into that class with those peers would not be a particularly strong student. I think acceleration at that level is often reserved for kids who will still be above average in the situation they are moving into. If you are in a smaller district with lower-performing students, it may make sense to even move him up 3 grades!! So much of what is relevant will have to do with your local conditions, plus the abilities of the teachers to fill gaps and/or compact parts of curriculum your child may already have been taught.
Good luck with your decision, and I guess my only advice is to pay attention to your local numbers/situation. If your schools are flooded with brilliant kids, you probably don't need to accelerate as much to get a rigorous math class, but if not, it can make a lot of sense.
